Periosteum: The periosteum is a fibrous thick, white, tough, and vascular, double membrane that surrounds the outside of bones. The prefix peri means "around" and osteum means bone. The outer layer of the periosteum is a tough, fibrous protective layer. The inner layer is the osteogenic layer and contains cells responsible for making new bone, osteoblasts, which are make new bone cells, and osteoclasts which break up and destroy bone. Together, the two types of cells regulate the amount of bone. The periosteum is firmly anchored to the bone by Sharpey's fibers. The fibers of the periosteum are continuous with the ligaments and tendons that are connected to it.